In this project we are attempting to test two fundamental hypotheses: that the rate of change in intracranial pressure is a major influence on the systemic manifestations observed at a given magnitude of intracranial pressure, and that carefully controlled ventilation further alters these systemic manifestations to a dynamically increasing intracranial pressure. In addition we anticipate that by carefully controlling ventilatory parameters we will be able to define the mechanisms involved in the cardiopulmonary manifestations to increased intracranial pressure. We are unaware of previous in-depth studies concerning the rate of change in intracranial pressure as a significant determinant of the systemic response to it. Mineral oil will be infused into the cisterna magna of dogs by slowly, but continuously elevating a drip chamber. In this manner intracranial pressure will constantly increase in relation to the height of the drip chamber. The chamber will be weighed continuously so that dynamic intracranial compliance can be calculated. The cardiopulmonary parameters to be monitored are chosen primarily to quantitate pulmonary gas exchange and myocardial performance. Both awake and anesthesized dogs will be employed in this project. This research not only adequately tests the aforementioned hypotheses but also will provide clinically relevant data. Of real significance is how should a patient with increased intracranial pressure be ventilated? We anticipate that these patients should not all be ventilated the same and that the data obtained in these experiments will be useful in making such decisions. The neurosurgical intensive care unit at this institution is currently being readied so that essentially all of the parameters monitored in these experiments can be monitored in patients so that the data obtained in the laboratory will be useful in managing such patients.